Volatile metal hydride compounds are widely used as precursors in chemical vapor deposition (CVD) processes for the manufacture of microelectronic components. The growth and quality of thin metallic films formed from metal hydride precursors are highly dependent upon the purity of the precursor compounds and require extremely low concentrations of impurities, particularly volatile sulfur-containing impurities.
Purification of metal hydride compounds typically is effected in batch processes using purification media such as adsorbents, getters, and other reactive materials. When the purification media becomes spent as indicated by the initial breakthrough of impurities in the treated product, the process equipment is taken off line, disassembled to remove spent purification media, and reassembled with fresh purification media. Because volatile metal hydride compounds (for example, arsine and phosphine) are highly toxic, it is desirable to maximize the operating time between changes of the purification media in order to minimize purification media replacement and reduce potential hazards to operating personnel. Because the concentration of impurities in the raw feed material may vary significantly from batch to batch, it is also desirable to utilize purification processes that maintain high removal efficiencies regardless of fluctuations in the level of feed impurities.
As purity requirements for metal hydride precursors used in CVD processes become more stringent, there is a need for improved methods for removing impurities from precursor feed materials, particularly when the impurities include volatile sulfur compounds. These improved processes should reduce the potential for personnel exposure to the precursors and also allow for wide swings in impurity concentration levels in the feed materials. These needs are addressed by embodiments of the present invention described below and defined by the claims that follow.